1. Field of the Invention
The present invention generally relates to the use of polyvinylidene difluoride containing copolymers as barrier materials wherein the gas diffusivity of the copolymer can be controlled. More particularly, the present invention relates to compositions where the composition of the copolymers defines the barrier properties.
2. Description of the Prior Art
Fluorine-containing monomers, polymers and copolymers are described in U.S. Pat. Nos. 2,970,988, 2,931,840, 2,996,555, 3,085,996, 6,486,281, 6,867,273 (see Column 3, line 29-50) and U.S. Pat. No. 6,703,450 (see Column 2, line 42, to Column 3, line 5, for monomers). Vinylidene fluoride copolymers are described in U.S. Pat. No. 3,893,987 and a process for making fluoroolefin copolymers is described in U.S. Pat. No. 3,240,757. Vinylidene fluoride/chlorotrifluoroethylene copolymers are described in U.S. Pat. Nos. 5,292,816 and 3,053,818. Vinylidene fluoride/3,3,3-trifluoro-2-trifluoromethylpropene copolymers and a method for making vinylidene fluoride/3,3,3-trifluoro-2-trifluoromethylpropene copolymers are described in U.S. Pat. No. 3,706,723.
Other copolymers made with fluoroolefins are described in U.S. Pat. Nos. 2,599,640; 2,919,263; 3,812,066; 4,943,473; 5,200,480; 6,342,569 and 6,361,641.
Fluorocarbon/Acrylate Coatings are described in U.S. Pat. No. 3,716,599 and powder coating are described in U.S. Pat. No. 5,030,394.
Solvent based blending is described in U.S. Pat. No. 3,324,069. Polyvinylidene fluoride/polymethyl methacrylate blends are described in U.S. Pat. No. 6,362,271. Other blends are described in U.S. Pat. Nos. 5,051,345; 5,496,889 (Compatibilized Blends); U.S. Pat. No. 4,990,406 (F-terpolymer/acrylate blends). Graft Copolymers are described in U.S. Pat. No. 4,308,359.
A wide variety of thermoplastic polymers are known, as are films formed from such thermoplastic polymers. Important physical characteristics of such films include their barrier properties, including barriers to gas, aroma, and/or vapor such as water vapor, as well as its physical characteristics, such as toughness, wear and weathering resistances, and light transmittance. These properties are especially important in film applications such as, for example, in the use of films as a packaging material for food or medical products.
It is well known in the art to produce multilayer fluoropolymers films. See, for example, U.S. Pat. Nos. 4,146,521; 4,659,625; 4,677,017; 5,139,878; 5,855,977; 6,096,428; 6,138,830; and 6,197,393. Many fluoropolymers materials are commonly known for their excellent moisture and vapor barrier properties, and therefore are desirable components of packaging films. In addition, fluoropolymers exhibit high thermal stability and excellent toughness.
Polychlorotrifluoroethylene has been employed as a high performance moisture barrier polymer. Comonomers, such as vinylidene fluoride, have been introduced to modify water permeation rate or other physical properties (WO 9306159 and U.S. Published Application No. 2007128393). Various fluorocopolymers, including copolymers of 2,3,3,3-tetrafluoro-1-propene and chlorotrifluoroethylene, were disclosed in U.S. Pat. No. 2,970,988 as useful in protective coatings and as elastomers.
There is a continuing need in the art for further improvements in fluoropolymers films and film structures, particularly those which provide a film structure featuring differentiated barrier performance for different gases and/or water vapor. This invention provides compositions showing specific controlled gas diffusivity for oxygen and for water vapor as defined by copolymer stoichiometry.
For this reason, the copolymer compositions and the processes for making these compositions according to the present invention are potentially useful commercially.